/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.solr.response;

import java.io.Writer;
import java.io.IOException;

import org.apache.solr.common.util.NamedList;
import org.apache.solr.request.SolrQueryRequest;
import org.apache.solr.util.plugin.NamedListInitializedPlugin;

/**
 * Implementations of <code>QueryResponseWriter</code> are used to format
 * responses to query requests.
 * 
 * Different <code>QueryResponseWriter</code>s are registered with the
 * <code>SolrCore</code>. One way to register a QueryResponseWriter with the
 * core is through the <code>solrconfig.xml</code> file.
 * <p>
 * Example <code>solrconfig.xml</code> entry to register a
 * <code>QueryResponseWriter</code> implementation to handle all queries with a
 * writer type of "simple":
 * <p>
 * <code>
 *    &lt;queryResponseWriter name="simple" class="foo.SimpleResponseWriter" /&gt;
 * </code>
 * <p>
 * A single instance of any registered QueryResponseWriter is created via the
 * default constructor and is reused for all relevant queries.
 * 
 * 
 */
public interface QueryResponseWriter extends NamedListInitializedPlugin {
	public static String CONTENT_TYPE_XML_UTF8 = "application/xml; charset=UTF-8";
	public static String CONTENT_TYPE_TEXT_UTF8 = "text/plain; charset=UTF-8";
	public static String CONTENT_TYPE_TEXT_ASCII = "text/plain; charset=US-ASCII";

	/**
	 * Write a SolrQueryResponse, this method must be thread save.
	 * 
	 * <p>
	 * Information about the request (in particular: formating options) may be
	 * obtained from <code>req</code> but the dominant source of information
	 * should be <code>rsp</code>.
	 * <p>
	 * There are no mandatory actions that write must perform. An empty write
	 * implementation would fulfill all interface obligations.
	 * </p>
	 */
	public void write(Writer writer, SolrQueryRequest request,
			SolrQueryResponse response) throws IOException;

	/**
	 * Return the applicable Content Type for a request, this method must be
	 * thread safe.
	 * 
	 * <p>
	 * QueryResponseWriter's must implement this method to return a valid HTTP
	 * Content-Type header for the request, that will logically correspond with
	 * the output produced by the write method.
	 * </p>
	 * 
	 * @return a Content-Type string, which may not be null.
	 */
	public String getContentType(SolrQueryRequest request,
			SolrQueryResponse response);

	/**
	 * <code>init</code> will be called just once, immediately after creation.
	 * <p>
	 * The args are user-level initialization parameters that may be specified
	 * when declaring a response writer in solrconfig.xml
	 */
	public void init(NamedList args);
}
